Frequency-domain Procedure Research Articles

Seismic Responses of an Isolated Long-span Bridge using Frequency Domain and Time Dependent Procedures

Seismic behavior of an isolated bridge is analyzed in the frequency domain under the effects of nonstationary ground motions. For dynamic solutions, different ground environments are considered by simulating nonstationary quakes that can be represented from bedrock to soft ground level. In the simulations, power spectral functions and filtered white noise model are adopted for spectral densities of the earthquake excitations. Various computer algorithms have been developed for earthquake simulations, establishing the bridge finite element model and stochastic solutions. Twenty simulated ground motions are used for each soil profile and the parameters of Rayleigh dispersion are estimated by evaluating the system responses for each ensemble. A number of peak response factors dependent on soil conditions are presented for seismic responses. In addition, extreme value distributions of the responses are shown with the probability of exceeding functions and tables. The responses are discussed for the specific exceedance level of probabilities used in probabilistic design process. The stochastic analyses generally yielded responses consistent with time domain solutions. Exceedance probability functions of the peak responses were obtained in a close relationship. However, the probability distributions of the responses decomposed for the soft soil case and they displayed a wider dispersion even for low exceedance levels. The peak responses are expressed with some exceedance probabilities. In the estimation of response variations, this study showed the practicality of the frequency domain method and the results revealed higher peak response factors and variances for softer soil conditions. Furthermore, this study indicated that the frequency domain procedure is an effective tool in the obtaining of nonstationary seismic responses.

A frequency-domain procedure to design TMDs for lively pedestrian structures considering Human–Structure Interaction

The use of advanced low-density high-strength materials, such as Fibre Reinforced Polymers (FRPs) or aluminium alloys, has enabled to construct lightweight and slender footbridges, which structural design may be governed by the Vibration Serviceability Limit State (VSLS) under human-induced loads. These structures may be excited in resonance by higher and less energetic harmonics of human actions in contrast to footbridges built with traditional construction materials. Additionally, Human–Structure Interaction (HSI) may be relevant on the dynamic response of these type of pedestrian structures. A solution for the aforementioned issues may be the installation of Tuned Mass Dampers (TMDs) in the bridge. Thus, this paper presents a frequency-domain procedure to design TMDs for lively pedestrian structures based on a coupled Human–Structure–controller system. The proposal, which accounts for uncertainties associated to the structure and the interaction phenomenon, is applied to design passive inertial control systems for an FRP footbridge. Also, the implications of HSI in the design of TMDs are discussed, and the performance of the designed devices is assessed considering two human actions, bouncing and walking. Since the peak value of the steady-state response of a pedestrian structure can be fast assessed through algebraic operations, the proposed approach is suitable to design robustly control systems against human-induced vibrations. As a result, structural elements and controllers can be properly dimensioned, leading to further cost-effective footbridge projects.

Unknown input observer for linear singular systems with variable delay: the continuous and the discrete time cases

In this paper, we propose a new approach to design a functional observer for linear singular systems with unknown inputs. Variable-Time delay is present in both state and input vectors. The proposed observer is developed in time and frequency domains. The time domain observer design is obtained for both continuous and discrete time systems. The procedure design is based on the unbiasedness of the estimation error dynamic of the observer using Lyapunov functional. The problem is solved by means of linear matrix inequalities to find the optimal gain implemented in the functional observer design. Frequency domain procedure is derived from time domain results, where we propose a suitable co-prime matrix fractions description. The main interest is that the proposed algorithm estimates both a functional state and the unknown input independently from the considered delay in time and frequency domains. The proposed observer proves its effectiveness on a given numerical example.

Vibration signature analysis of coffee beans processing Machineries

It is practical that Major research in the analysis of rolling elements was carried out in the case of one-point defects. For multiple and generalized defect diagnosis, there is a lot of flexibility. The vibration signals for various machines with faulty rolling component bearings are composed & analyzed using vibration signature analysis techniques in this study. Multiple defects on bearing components are used to test the test bearings. The use of vibration signature analysis methods to identify faults in rolling aspect bearings by means of time & frequency domain procedures is investigated in order to determine the best method for fault discovery in the case of several faults in bearing machinery. The feature extracted in this study is expected to be useful in the development of automated fault diagnostics systems for bearing components with multiple defects. In This work we have applied vibration signature analyses on the ball bearings of coffee processing machines and evaluated the results.

Proposed framework for cancelable face recognition system

This paper suggests two novel presented cancellable biometric realization approaches recognition and template protection. In the suggested scheme, the A Trous Transform (AT) algorithm is applied on the face images. Then the AT divides the image into seven subbands. The resultant map is encrypted with the Homomorphic Filtering Masking (HFM) encoding algorithm is utilized for cancelable face recognition system. Then the second HFM utilized is produced from the image. This technique can be used to advance a frequency domain procedure for making this system for biometric template protection. The second algorithm presents a new technique to detect the features for Facial Expression Recognition (FER). This technique is established on segmentation process by Canny Edge Detection (CD) and Hough Transform (HT) with the number of feature points as the key parameters for classification. This algorithm is set up analysis the FER with the number of HT feature points as the key parameters for classification. Simulation results using evaluation metrics False Positive Rate (FPR), False Negative Rate (FNR), Equal Error Rate (EER), Receiver Operating Characteristic (ROC) and Area under ROC (AROC) prove that the first proposed cancelable biometric technique with the second key are best with comparing the other keys.The obtained results clear that the second suggested technique has sucesseded in detection the features of FER for sad, happy, neutral, angry, disgust, fear, surprise cases and the face positions.

An Experimental Study on the Defect Detectability of Time- and Frequency-Domain Analyses for Flash Thermography

A defect’s detectability in flash thermography is highly dependent on the applied post-processing methodology. The majority of the existing analysis techniques operate either on the time-temperature data or on the frequency-phase data. In this paper, we compare the efficiency of time- and frequency-domain analysis techniques in flash thermography for obtaining good defect detectability. Both single-bin and integrated-bin evaluation procedures are considered: dynamic thermal tomography and thermal signal area for the time-domain approach, and frequency domain tomography and adaptive spectral band integration for the frequency-domain approach. The techniques are applied on various carbon fiber reinforced polymer samples having a range of defect sizes and defect types. The advantages and drawbacks of the different post-processing techniques are evaluated and discussed. The best defect detectability is achieved using the integrated procedure in frequency domain.

Implementation face based cancelable multi-biometric system

This paper suggests novel two proposed cancellable biometric realization techniques recognition and template protection. In this paper, the Homomorphic Key (HK) encoding algorithm is utilized for cancelable face system. In the first suggested scheme, the HK algorithm is applied on the face images. The resultant map is encrypted, in order to the second HK utilized in the HK is produced from the image. This approach can be used to develop a frequency domain procedure for making this system for biometric template protection. The second algorithm presents a new approach to detect the features of face images depending the Speeded Up Robust Features (SURF) and Optimum Global Thresholding (OTSU) method. This algorithm is relied on scale space analysis with the number of SURF feature points as the key parameters for classification. Simulation results using evaluation metrics False Positive Rate (FPR), False Negative Rate (FNR), Equal Error Rate (EER), Receiver Operating Characteristic (ROC) and Area under ROC (AROC) prove that the first proposed cancelable biometric technique with the second key are best with comparing the other keys. The obtained results clear that the second suggested technique has sucesseded in detection the features of the skin, eyes, nose, hair, ears images and the face positions.

Finite locally resonant metafoundations for the protection of slender storage tanks against vertical ground accelerations

Inspired by recent findings in the field of Metamaterials, finite lattice locally resonant metafoundations represent an innovative solution for the seismic protection of storage tanks. One of the advantages with respect to traditional rubber bearings is the possibility of protecting the structure against the vertical component of ground accelerations, which has a significant influence on the hydrodynamic pressure of tanks. In this respect, we propose feasible configurations for a finite lattice metafoundation formed by steel columns, concrete slabs and concrete resonators, which allow for the protection of a slender tank against earthquakes with a significant vertical component. Based on the acceleration response variance of the liquid mass involved in the breathing mode, we develop an optimization procedure in frequency domain, which is adopted to design resonators stiffness and damping ratio. Time history analyses validate the efficacy of the proposed systems and show that staggering the columns at the second level of the outer frame allows for a higher attenuation of base pressure; it can decrease by 22.7% and 23.3% for OBE and SSE earthquakes, respectively. Eventually, we investigate the relationships between seismic signals frequency content and dynamic properties of coupled foundation-tank systems.

Advances in spatial analog optical computing devices

Spatial analog optical computing devices possess the capability of high-throughput, real-time and low-energy information processing. Optical metamaterials, which are ultracompact in structure and possess powerful ability to control the light, can be utilized to establish miniatured and integrated spatial analog optical computing devices. The methods of designing the spatial analog optical computing devices could be mainly classified as two kinds—4F system method and Green’s function method. The 4F system method requires two Fourier transform lenses and a spatial frequency filter, where the actual computing procedure is performed in the spatial domain. The 4F system is usually bulky and complicated. The Green’s function method directly leverages the nonlocal response of the carefully tailored optical materials to implement analog computing procedure in the spatial frequency domain and its structure is compact without extra Fourier transform components. Research advances in spatial analog optical computing devices by using these two methods for the last few years are introduced in this paper. These researches could be classified as differentiators, integrators, equation solvers and spatial frequency filters according to the standard of computing functions. The approaches to designing these devices are further demonstrated. Then, computing devices which could realize spatial analog first-order difference by use of the spin-orbit interaction proposed recently are introduced. Finally, application fields and study prospects of spatial analog optical computing devices are discussed and summarized.

Exploring the Connected Brain by fNIRS: Human-to-Human Interactions Engineering

Functional Near Infrared Spectroscopy (fNIRS) is a relatively new neuroimagingtechnique adequate and useful for exploring neural activity in social contexts involving humaninteractions. Compared to functional Magnetic Resonance Imaging (fMRI), fNIRS is easy-to-usesafe, noninvasive, silent, relatively low cost and portable, and applicable to subjects of all ages, thusresulting in a good option for ecological studies involving humans in their real-life context.Moreover, by using hyperscanning technique, fNIRS allows recording the hemodynamic cerebralactivity of two interacting subjects in an ecological context or during a shared performance. Thus,moving from a simple analysis about each subject’s neural response during joint actions towardsmore complex computations makes possible to investigate brain synchrony, that is the if and howone’s brain activity is related to that of another interacting partner simultaneously recorded. Here,we discuss how connectivity analyses, with respect to both time and frequency domain procedures,permitted to deepen some aspects of inter-brain synchrony in relation to emotional closeness, and tohighlight how concurrent, cooperative actions can lead to interpersonal synchrony and bondconstruction.

A fragmented-periodogram approach for clustering big data time series

We propose and study a new frequency-domain procedure for characterizing and comparing large sets of long time series. Instead of using all the information available from data, which would be computationally very expensive, we propose some regularization rules in order to select and summarize the most relevant information for clustering purposes. Essentially, we suggest to use a fragmented periodogram computed around the driving cyclical components of interest and to compare the various estimates. This procedure is computationally simple, but able to condense relevant information of the time series. A simulation exercise shows that the smoothed fragmented periodogram works in general better than the non-smoothed one and not worse than the complete periodogram for medium to large sample sizes. We illustrate this procedure in a study of the evolution of several stock markets indices. We further show the effect of recent financial crises over these indices behaviour.

Time-domain approach for multi-exciter random environment test

This paper presents a time-domain method for multi-exciter random environment tests. Traditional random environment test theory has been formulated in the frequency domain, where an important step is taking the inverse of the frequency response function matrices (FRFMs). The accuracy of this inversion tends to be poor, particularly at frequencies near lightly damped resonances. The currently used control algorithms face difficulties in suppressing abnormal spectral lines caused by this inverse problem. In this paper, traditional formulations of the environment test are reformed, and the time-domain method is adopted; this results in a more precise inverse operation in environment tests. To achieve this, reference spectra are converted into time-domain response signals. The finite long driving signals are derived by the state-space method with estimated state vectors. During the process, the inverse of rank-deficient Toeplitz matrices are stabilized with truncated singular value decomposition (TSVD) to suppress all abnormally high-level components in the driving forces; thus, overall, the spectra lines produced by noise within the frequency band are filtered out. A numerical simulation of a single-axis random vibration test of a cantilever beam is conducted using the traditional frequency-domain procedure (FDP) and the proposed time-domain procedure (TDP). The response spectra generated by both procedures are tested by control algorithms, and the result shows that responses generated by the proposed TDP are more easily controlled. The conditions of stability for both the FDP and the TDP are also determined and introduced in the simulation. Moreover, a multi-axis vibration experiment further validates the effectiveness of the TDP.

A concise account of techniques available for shipboard sea state estimation

This article gives a review of techniques applied to make sea state estimation on the basis of measured responses on a ship. The general concept of the procedures is similar to that of a classical wave buoy, which exploits a linear assumption between waves and the associated motions. In the frequency domain, this assumption yields the mathematical relation between the measured motion spectra and the directional wave spectrum. The analogy between a buoy and a ship is clear, and the author has worked on this wave buoy analogy for about fifteen years. In the article, available techniques for shipboard sea state estimation are addressed, but with a focus on only the wave buoy analogy. Most of the existing work is based on methods established in the frequency domain but, to counteract disadvantages of the frequency-domain procedures, newer studies are working also on procedures formulated directly in the time domain. Sample results from several studies are included, and the main findings from these are mentioned.

Homomorphic filtering textural analysis technique to reduce multiplicative noise in the 11Oba nano-doped liquid crystalline compounds

The compound undecyloxy benzoic acid (11Oba) exhibits nematic and smectic-C phases while a nano-doped undecyloxy benzoic acid with ZnO exhibits the same nematic and smectic-C phases with reduced clearing temperature as expected. The doping is done with 0.5% and 1% ZnO molecules. The clearing temperatures are reduced by approximately 4 ° and 6 °, respectively (differential scanning calorimeter data). While collecting the images from a polarizing microscope connected with hot stage and camera, the illumination and reflectance combined multiplicatively and the image quality was reduced to identify the exact phase in the compound. A novel technique of homomorphic filtering is used in this manuscript through which multiplicative noise components of the image are separated linearly in the frequency domain. This technique provides a frequency domain procedure to improve the appearance of an image by gray level range compression and contrast enhancement.

Theoretical Analysis and Experimental Validation of a Simplified Fractional Order Controller for a Magnetic Levitation System

Fractional order (FO) controllers are among the emerging solutions for increasing closed-loop performance and robustness. However, they have been applied mostly to stable processes. When applied to unstable systems, the tuning technique uses the well-known frequency-domain procedures or complex genetic algorithms. This brief proposes a special type of an FO controller, as well as a novel tuning procedure, which is simple and does not involve any optimization routines. The controller parameters may be determined directly using overshoot requirements and the study of the stability of FO systems. The tuning procedure is given for the general case of a class of unstable systems with pole multiplicity. The advantage of the proposed FO controller consists in the simplicity of the tuning approach. The case study considered in this brief consists in a magnetic levitation system. The experimental results provided show that the designed controller can indeed stabilize the magnetic levitation system, as well as provide robustness to modeling uncertainties and supplementary loading conditions. For comparison purposes, a simple PID controller is also designed to point out the advantages of using the proposed FO controller.

Lorenz gauge gravitational self-force calculations of eccentric binaries using a frequency domain procedure

We present an algorithm for calculating the metric perturbations and gravitational self-force for extreme-mass-ratio inspirals (EMRIs) with eccentric orbits. The massive black hole is taken to be Schwarzschild and metric perturbations are computed in Lorenz gauge. The perturbation equations are solved as coupled systems of ordinary differential equations in the frequency domain. Accurate local behavior of the metric is attained through use of the method of extended homogeneous solutions and mode-sum regularization is used to find the self-force. We focus on calculating the self-force with sufficient accuracy to ensure its error contributions to the phase in a long term orbital evolution will be $\delta\Phi \lesssim 10^{-2}$ radians. This requires the orbit-averaged force to have fractional errors $\lesssim 10^{-8}$ and the oscillatory part of the self-force to have errors $\lesssim 10^{-3}$ (a level frequently easily exceeded). Our code meets this error requirement in the oscillatory part, extending the reach to EMRIs with eccentricities of $e \lesssim 0.8$, if augmented by use of fluxes for the orbit-averaged force, or to eccentricities of $e \lesssim 0.5$ when used as a stand-alone code. Further, we demonstrate accurate calculations up to orbital separations of $a \simeq 100 M$, beyond that required for EMRI models and useful for comparison with post-Newtonian theory. Our principal developments include (1) use of fully constrained field equations, (2) discovery of analytic solutions for even-parity static modes, (3) finding a pre-conditioning technique for outer homogeneous solutions, (4) adaptive use of quad-precision and (5) jump conditions to handle near-static modes, and (6) a hybrid scheme for high eccentricities.

Definitions and frequency domain procedures for dynamic data analysis

This paper contains definitions, notation and computational procedures recommended for analyzing dynamic data properties of stationary or transient random data, including their passage through physical systems.

Comparative study of two global affine Linear Periodic Parameter Varying State Space model estimation algorithms

Abstract A comparative study is made between two global Linear Periodic Parameter-Varying (LPPV) identification algorithms. The first method is a state-of-the-art subspace identification method in the time domain. The second is a newly developed frequency domain approach, where the identification experiment is designed carefully so we can exploit the resulting structure. For both methods, the result is a state space model with an affine dependence on the varying parameters, which can be used for LPV control synthesis. Simulations show that the frequency domain procedure has a lower variance for identical experimental conditions.

Lorenz gauge gravitational self-force calculations of eccentric binaries using a frequency domain procedure

Lorenz gauge gravitational self-force calculations of eccentric binaries using a frequency domain procedure

Evaluation of mechanical component fatigue behavior under random loads: Indirect frequency domain method

The fatigue behavior assessment for mechanical components subjected to random loads is traditionally conducted in time domain. An alternative frequency domain procedure is applicable under the hypothesis of stationary Gaussian stress state. The main objectives of this work consist in the description of the limits of applicability for the frequency domain methods and in the proposal of an original procedure (indirect method), that combines the advantages of the dynamic analysis conducted in the frequency domain, with the fatigue direct assessment criteria in time domain. Due to the stochastic nature of the fatigue damage under random stresses, a deterministic approach cannot be adopted, however, according to the common practice, a mean value of the damage can be assessed, paying attention that the time history used is sufficiently long. This makes sure the random error is negligible as it is of the same order of magnitude of the other approximations contained in the simulation process. In this paper the authors investigate under which hypothesis this method is valid and they propose a tool for the significance test of time data with regards to their capability in reproducing the right fatigue cycle amplitude distribution of the specific random process.